as disclosed in Japanese Patent Public Disclosure No. 267550/86. This process, as illustrated by the following reaction scheme (1), comprises reacting the compound of formula (II) with 1-bromo-3-propene in the presence of a basic catalyst to form a 20S-(3-butenyloxy) compound, oxidizing the 20S-(3-butenyloxy) compound with oxygen in the presence of a catalyst to obtain a 20S-(3-oxobutyloxy) compound, and reacting the 208-(3-oxobutyloxy) compound with a Grignard reagent to obtain a 20S-(3-hydroxy-3-methylbutyloxy) compound. ##STR3##
However, the above process requires complicated operation. In addition, since the reaction between the compound (II) and 1-bromo-3-propene is attended by by-production of a 20S-(2-butenyloxy) compound in a considerable proportion, resulting in a low yield of the desired compound, and separation and purification of the desired compound involves difficulty.